Revert "fix #15836 proc arg return type auto unexpectly match proc with concr…" (#21057)

Revert "fix #15836 proc arg return type auto unexpectly match proc with concr… (#21044)"

This reverts commit 0cd9bdcf9f6802421e0d8e4c28fc732012af605e.

9 files changed, 12 insertions, 23 deletions

diff --git a/compiler/ast.nim b/compiler/ast.nim
index 198d21bea..9679c10c1 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -2047,9 +2047,6 @@ template detailedInfo*(sym: PSym): string =
 proc isInlineIterator*(typ: PType): bool {.inline.} =
   typ.kind == tyProc and tfIterator in typ.flags and typ.callConv != ccClosure
 
-proc isIterator*(typ: PType): bool {.inline.} =
-  typ.kind == tyProc and tfIterator in typ.flags
-
 proc isClosureIterator*(typ: PType): bool {.inline.} =
   typ.kind == tyProc and tfIterator in typ.flags and typ.callConv == ccClosure
 
diff --git a/compiler/docgen.nim b/compiler/docgen.nim
index 0a24d2e09..e2c04430c 100644
--- a/compiler/docgen.nim
+++ b/compiler/docgen.nim
@@ -558,7 +558,7 @@ proc runAllExamples(d: PDoc) =
 
 proc quoted(a: string): string = result.addQuoted(a)
 
-proc toInstantiationInfo(conf: ConfigRef, info: TLineInfo): (string, int, int) =
+proc toInstantiationInfo(conf: ConfigRef, info: TLineInfo): auto =
   # xxx expose in compiler/lineinfos.nim
   (conf.toMsgFilename(info), info.line.int, info.col.int + ColOffset)
 
diff --git a/compiler/lookups.nim b/compiler/lookups.nim
index df5a5333e..2121982a6 100644
--- a/compiler/lookups.nim
+++ b/compiler/lookups.nim
@@ -422,7 +422,7 @@ type SpellCandidate = object
   msg: string
   sym: PSym
 
-template toOrderTup(a: SpellCandidate): (int, int, string) =
+template toOrderTup(a: SpellCandidate): auto =
   # `dist` is first, to favor nearby matches
   # `depth` is next, to favor nearby enclosing scopes among ties
   # `sym.name.s` is last, to make the list ordered and deterministic among ties
diff --git a/compiler/sem.nim b/compiler/sem.nim
index 1f8e217b3..a1388bd87 100644
--- a/compiler/sem.nim
+++ b/compiler/sem.nim
@@ -81,7 +81,7 @@ template semIdeForTemplateOrGeneric(c: PContext; n: PNode;
 proc fitNodePostMatch(c: PContext, formal: PType, arg: PNode): PNode =
   let x = arg.skipConv
   if (x.kind == nkCurly and formal.kind == tySet and formal.base.kind != tyGenericParam) or
-    (x.kind in {nkPar, nkTupleConstr}) and formal.kind notin {tyUntyped, tyBuiltInTypeClass, tyAnything}:
+    (x.kind in {nkPar, nkTupleConstr}) and formal.kind notin {tyUntyped, tyBuiltInTypeClass}:
     changeType(c, x, formal, check=true)
   result = arg
   result = skipHiddenSubConv(result, c.graph, c.idgen)
@@ -439,7 +439,7 @@ proc semAfterMacroCall(c: PContext, call, macroResult: PNode,
       # does not mean we expect a tyTypeDesc.
       retType = retType[0]
     case retType.kind
-    of tyUntyped, tyAnything:
+    of tyUntyped:
       # Not expecting a type here allows templates like in ``tmodulealias.in``.
       result = semExpr(c, result, flags, expectedType)
     of tyTyped:
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index a467c408a..22a247ceb 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -1913,8 +1913,8 @@ proc semProcBody(c: PContext, n: PNode; expectedType: PType = nil): PNode =
     else:
       localError(c.config, c.p.resultSym.info, errCannotInferReturnType %
         c.p.owner.name.s)
-  if isIterator(c.p.owner.typ) and c.p.owner.typ[0] != nil and
-      c.p.owner.typ[0].kind == tyAnything:
+  if isInlineIterator(c.p.owner.typ) and c.p.owner.typ[0] != nil and
+      c.p.owner.typ[0].kind == tyUntyped:
     localError(c.config, c.p.owner.info, errCannotInferReturnType %
       c.p.owner.name.s)
   closeScope(c)
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index d19d75611..a006013b8 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -2179,7 +2179,8 @@ proc semProcAux(c: PContext, n: PNode, kind: TSymKind,
     if hasProto: localError(c.config, n.info, errImplOfXexpected % proto.name.s)
     if {sfImportc, sfBorrow, sfError} * s.flags == {} and s.magic == mNone:
       # this is a forward declaration and we're building the prototype
-      if s.kind in {skProc, skFunc} and s.typ[0] != nil and s.typ[0].kind == tyAnything:
+      if s.kind in {skProc, skFunc} and s.typ[0] != nil and s.typ[0].kind == tyUntyped:
+        # `auto` is represented as `tyUntyped` at this point in compilation.
         localError(c.config, n[paramsPos][0].info, "return type 'auto' cannot be used in forward declarations")
 
       incl(s.flags, sfForward)
diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index dca0d753b..3eaf29755 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -1405,7 +1405,9 @@ proc semProcTypeNode(c: PContext, n, genericParams: PNode,
             "' is only valid for macros and templates")
       # 'auto' as a return type does not imply a generic:
       elif r.kind == tyAnything:
-        discard
+        # 'p(): auto' and 'p(): untyped' are equivalent, but the rest of the
+        # compiler is hardly aware of 'auto':
+        r = newTypeS(tyUntyped, c)
       elif r.kind == tyStatic:
         # type allowed should forbid this type
         discard
diff --git a/tests/proc/tillegalreturntype.nim b/tests/proc/tillegalreturntype.nim
index 1076f7f75..799cad53a 100644
--- a/tests/proc/tillegalreturntype.nim
+++ b/tests/proc/tillegalreturntype.nim
@@ -1,5 +1,5 @@
 discard """
-  cmd: "nim check --hints:off $file"
+  cmd: "nim check $file"
   errormsg: ""
   nimout: '''
 tillegalreturntype.nim(11, 11) Error: return type 'typed' is only valid for macros and templates
diff --git a/tests/types/t15836.nim b/tests/types/t15836.nim
deleted file mode 100644
index 9c0c26dec..000000000
--- a/tests/types/t15836.nim
+++ /dev/null
@@ -1,11 +0,0 @@
-discard """
-  errormsg: "type mismatch: got <string> but expected 'int'"
-  line: 11
-""" 
-
-proc takesProc[T](x: T, f: proc(x: T): int) =
-    echo f(x) + 2
-
-takesProc(1, proc (a: int): int = 2) # ok, prints 4
-takesProc(1, proc (a: auto): auto = 2) # ok, prints 4
-takesProc(1, proc (a: auto): auto = "uh uh") # prints garbage